Acetic acid is a major metabolic product of bacteria which anaerobically decompose complex organic materials. In certain natural microbial ecosystems and in those used by man for waste treatment the strictly anaerobic microorganism Methanosarcina barkeri is of prime importance in subsequent conversion of acetic acid to methane and carbon dioxide. The enzymes involved in acetic acid metabolism have been studied in this project since detailed information about this process is lacking. Steps involved in cleavage of the carbon-carbon bond of acetate have been studied by analysis of the enzyme carbon monoxide dehydrogenase (CODH). Subsequent methyl group transfer steps are involved prior to methane formation and previously this project has identified, purified, and produced antibodies against two methyl group transferase enzymes. One of these is present largely in cells grown on methanol, and the other is predominant in cells capable of acetate conversion to methane and carbon dioxide. Studies on these enzymes have been extended in order to compare their structural and catalytic properties in detail.